1. Field of the Invention
The present invention relates to a polishing machine for polishing a workpiece such as a wafer.
2. Description of Related Art
A semiconductor device production process often employs a polishing process such as a CMP (chemical mechanical polishing) process. After an inter-level dielectric film and copper interconnections are formed on a surface of a wafer, for example, the CMP process is performed for planalization of surfaces of the inter-level dielectric film and the copper interconnections.
The schematic construction of a prior-art polishing machine is diagrammatically shown in FIG. 6. The polishing machine comprises: a wafer carrier 91 to be driven to be rotated about a vertically extending rotation axis thereof while holding a wafer W face down by suction; a polishing plate 92 provided below the wafer carrier 91 in an opposed relation thereto; and a nozzle 93 for supplying an abrasive agent to the polishing plate 92. The polishing plate 92 includes a generally circular base 94 having a greater size than the wafer W as viewed in plan and an abrasive pad 95 fixed to an upper surface of the base 94, and is adapted to be driven to be rotated about a vertically extending rotation axis thereof.
With this arrangement, a load is applied downward to the wafer carrier 91 to press the wafer W against the abrasive pad 95. In this state, the wafer carrier 91 and the polishing plate 92 are driven to be rotated while the abrasive agent is supplied onto the upper surface of the abrasive pad 95 from the nozzle 93. Thus, the surface of the wafer W (opposed to the polishing plate 92) can be polished.
The abrasive pad 95 rotated with the polishing plate 92 has different moving speeds at different positions thereof, depending on a radial distance from the center of the rotation of the abrasive pad 95 (polishing plate 92). Similarly, the wafer W rotated with the wafer carrier 91 has different moving speeds at different positions thereof, depending on a radial distance from the center of the wafer W. Therefore, the moving speed of the abrasive pad 95 relative to the different positions of the wafer W is not uniform, resulting in nonuniform polishing rate over the surface of the wafer W.
It is an object of the present invention to provide a polishing machine which is capable of uniformly polishing a workpiece.
A polishing machine according to the present invention comprises: a plurality of bases operative independently of each other; a plurality of abrasive pads respectively fixed to the plurality of bases and each having an abrasive surface for polishing a workpiece; and a base driving mechanism for individually operating the plurality of bases. The polishing machine preferably further comprises a control circuit for controlling the base driving mechanism so as to individually control the operations of the respective bases.
The plurality of bases may each be adapted to be rotated about an axis extending through a center thereof, or to be swung in a circular orbit about an axis extending through a point other than the center thereof. Alternatively, the plurality of bases may be adapted to linearly move the abrasive pads fixed thereto along the abrasive surfaces.
In accordance with the invention, the operations of the respective bases are individually controlled so that the abrasive pads are moved at a uniform speed with respect to different points on the workpiece and uniformly apply a pressure onto the different points on the workpiece. Thus, the workpiece can uniformly be polished.
A polishing machine according to another aspect of the invention comprises an abrasive pad having an abrasive surface for polishing a workpiece, the abrasive pad being adapted to be rotated about an axis extending through a center of the abrasive surface with the abrasive surface kept in abutment against the workpiece for polishing the workpiece, wherein the abrasive pad is divided into a center portion including the center of the abrasive surface and a ring portion surrounding the center portion.
Where the abrasive pad is a unitary member, the workpiece is liable to be polished at nonuniform polishing rate when the abrasive pad is rotated about the axis extending through the center of the abrasive surface thereof. This is because the abrasive surface of the abrasive pad has different moving speeds at different positions thereof, depending on a radial distance from the center of the abrasive surface.
In the present invention, the abrasive pad is divided into the center portion including the center of the abrasive surface and the ring portion surrounding the center portion. Therefore, the abrasive surface of the abrasive pad can be moved at a generally uniform moving speed by individually controlling the rotation of the center portion and the rotation of the ring portion. Thus, the polishing operation can be performed at a uniform polishing rate over the workpiece.
The polishing machine may further comprise an abrasive agent supply mechanism for supplying an abrasive agent necessary for the polishing of the workpiece onto the abrasive surface of the abrasive pad. In this case, the abrasive agent supply mechanism is preferably adapted to supply the abrasive agent onto the abrasive surface of the abrasive pad through a space between the plurality of abrasive pads or through a space between the center portion and the ring portion.
The abrasive surface of the abrasive pad is preferably formed with a recess for retaining the abrasive agent supplied from the abrasive agent supply mechanism.
With this arrangement, a portion of the abrasive agent supplied to the surface of the abrasive pad from the abrasive agent supply mechanism can be retained in the recess so as to be used for the polishing operation.
The foregoing and other objects, features and effects of the present invention will become more apparent from the following description of the preferred embodiments with reference to the attached drawings.